West Nile (WN) virus is a flavivirus that can cause fatal human encephalitis. Over the past four years, this virus has established itself across the United States. There are no approved vaccines or therapies to protect against WN virus. This project is designed to develop an effective anti-WN virus RNA interference therapy. Our hypothesis is that small interfering RNAs (siRNAs) targeting WN virus RNAs for degradation will inhibit viral replication and dissemination in vivo. Several siRNAs that inhibit WN virus in cultured cells will be identified in screening assays. The siRNAs showing robust interference in cellular assays will be evaluated in vivo using an established model of WN virus infection. The siRNAs will be expressed from adenovirus-associated virus vectors, including vectors designed to selectively target WN virus-infected cells. The AAV vectors will express siRNAs in mouse spleen, liver and brain, organs susceptible to WN virus. After WN virus challenge, the mice will be assessed for viral burden in different organs, and observed for morbidity, mortality. These experiments will provide the basis for Phase II experiments optimizing delivery of interfering RNAs to infected organs in animal models of WN virus infection. [unreadable] [unreadable]